1. Field of the Invention
This invention relates to a medical device and method for automatically determining the correct airflow pressure to be used for the treatment of a serious breathing problem during sleep known as obstructive sleep apnea. It is known that obstructive sleep apnea can be prevented by passing air into the nasal passages at an elevated pressure. This elevated pressure, administered using nasal-continuous-positive-airway-pressure (nasal-CPAP) equipment, prevents the upper airway from collapsing during sleep and therefore prevents the obstructive sleep apnea. In the invention, a microprocessor-controlled all-solid-state physiological monitoring and actuating device, automatically controls and manipulates the airflow pressure administered by the nasal-CPAP equipment while the patient is asleep, while simultaneously measuring and recording a variety of physiological parameters. After the sleep period, the recorded data are analyzed, and the changes in those physiological parameters are related to the airflow pressure. These parameters are measured while the nasal CPAP pressure is below, at, and above, the optimum value for preventing the obstructive sleep apnea. In this way, it is possible to determine the effect of the various airflow pressure levels on the obstructive sleep apnea, and to select the optimum nasal-CPAP airflow pressure for that patient.
Previous methods for determining the correct airflow pressure involved continuous supervision and observation of the patient, with the airflow pressure being manually increased until no further breathing abnormalities or evidence of upper airway resistance are observed. Many different devices can monitor vital signs and correlate the recorded data with the patient's respiratory function. Some devices have the capability of modifying the patient's breathing. However, no other devices automatically control the pressure of the inspired or expired air, and change that pressure in response to the measured vital signs in order to determine the optimum airflow pressure to be used in a therapeutic device.
2. Description of Sleep Apnea
Sleep apnea syndrome is an often serious breathing disorder during sleep characterized by repeated episodes of apnea (cessation of breathing) typically lasting 20-60 seconds in duration. The disorder is often associated with hypoxemia, cardiac arrhythmias, hypertension, disturbed nocturnal sleep, and symptoms such as excessive daytime sleepiness and cognitive impairment. The most common form of sleep apnea is associated with a collapse of the upper airway in the hypopharynx or posterior oropharynx, causing a partial or complete obstruction to the passage of air. After the airway becomes obstructed, it is common for the patient to make little or no effort to breathe, but eventually the patient makes increasing efforts to inspire and expire with excessive fluctuations in intrathoracic pressure. Nevertheless, the obstruction is usually not relieved until the patient has had a brief partial arousal from sleep.